Low mitotic count may affect the prognosis of uterine leiomyosarcoma: A report of two cases.

Introduction: Uterine leiomyosarcoma (uLMS) is characterized by its aggressive nature, early metastatic potential, and poor clinical outcomes. Diagnosis of uLMS requires two out of the following three diagnostic criteria: marked cytologic atypia, 10 mitoses per 10 high power fields, tumor cell necrosis. This case series presents two cases of uLMS with a low mitotic rate and an indolent disease course, with excellent response to hormone therapies. Case 1: A 44-year-old female was diagnosed with uLMS following a supracervical hysterectomy in 2006. The primary tumor demonstrated tumor cell necrosis, cytologic atypic, and 6 mitoses per 10 HPF. Her 18-year disease course is notable for four debulking surgeries and multiple courses of hormonal therapy resulting in durable responses. Case 2: A 75-year-old female was diagnosed with smooth muscle tumor of uncertain malignant potential (STUMP) status post debulking surgery which was revised to leiomyosarcoma following lung biopsy confirmation of metastasis. The primary tumor and lung biopsy demonstrated tumor cell necrosis, cytologic atypia and 2 mitosis per 10 HPF. She demonstrated stable disease on letrozole for 11 months. Discussion: These cases demonstrate that uLMS with low mitotic activity may exhibit less aggressive behavior than typical high-grade sarcomas. Recognizing this distinction can guide prognostication and treatment selection.